Canon printers have waste ink absorbers to soak up the ink after a cleaning cycle. Printers count the number of cycles you perform and show a warning when the ink pads are getting full. The printer will quit working after enough cycles to prevent the pads from overflowing. Replacing the absorbent pads is a job that you can do yourself to save the expense of sending the printer to a repair shop.
Turn the printer off and remove the power cord. Disconnect the printer from your computer.
Remove the cover from the parallel port. Pry the cover off by placing a flathead screwdriver in the bottom slot and gently applying pressure to the back of the slot. The parallel port is where you plug the USB cable into the printer.
Reach inside the printer and bend the front two tabs holding the top while you lift the printer cover gently. Stop lifting the cover when the cover is above the tabs.
Use your screwdriver to push gently on the back two tabs while you lift the printer's cover off.
Remove the four screws holding the printer to the base and lift the printer off the base. Set the printer aside on a level surface. If the printer has a power module, slide it out the back before you remove the screws.
Put on rubber gloves.
Remove the old ink absorber and rinse the printer bottom off with hot water. Dry the bottom completely with paper towels. The waste ink absorber is a felt pad sitting on the printer base.
Place the new absorber in the printer bottom and reassemble the printer.
Reconnect the power cord and turn on the printer.
Reset the waste ink absorber levels using the method for your printer (see Resources).
You can order new waste ink absorbers from Canon by calling 1-800-385-2155. It is possible to wash old absorbers out and reuse them. You cannot get them clean again but you can remove most of the ink they contain. You must wait until the pads are completely dry before you reinstall and drying can take several days. If you decide to clean your old pads, you can use running hot water or mix a cleaning solution by combining one part clear ammonia (no suds), four parts Isopropanol and five parts distilled water and soak the pads to loosen any dried ink.
If you do not reset the "Waste Ink Absorber Full" warning, the printer will quit working after a few cleaning cycles. Replacing the pads alone does not reset the levels. Open windows and use fans if you use the cleaning solution to soak the pads. The fumes can be dangerous if you inhale them.